(1) Field of the invention
The present invention relates to a system and method for detecting an engine revolution speed, identifying each of cylinders, and controlling an engine operation according to the detected engine revolution speed and identified cylinder applicable to an internal combustion engine, particularly for a multi-cylinder, four-cycle, spark-ignited engine.
(2) Background of the art
In spark-ignited four-cycle internal combustion engines, various types of crank angle sensors of an electromagnetic pick-up type and of a photo-electric type using photo-electric elements have been used in a previously proposed fuel injection quantity and/or ignition timing controlling system.
One of the various types of the crank angle sensors, e.g., the photo-electric element type is exemplified by Japanese Patent Application--First Publications No. Showa 60-98171 published on June 1, 1985 and No. Showa 60-261978 published on Dec. 25, 1985.
Furthermore, the previously proposed crank angle sensor described above is also exemplified by U.S. Pat. No. 4,656,993 issued on April 14, 1987 and No. 4,747,389 issued on May 31, 1988.
The crank angle sensor disclosed in the above-identified Japanese Patent Application--First Publications is built in a spark ignition distributor and includes a plurality of first slits formed on an outer periphery of a rotor plate which revolves in synchronization with a crankshaft of the engine for detecting crank angular positions.
In addition, the crank angle sensor includes a second slit formed on an inner periphery of the rotor plate for discriminating each cylinder (cylinder number to be ignited).
Furthermore, the crank angle sensor picks up two signals (pulse trains) from the respective first and second slits and outputs the picked up signals to a microcomputer.
The microcomputer, then, carries out an ignition timing control in a fixed ignition timing mode or in a variable ignition timing control mode and fuel injection quantity control on the basis of the above-described, picked-up pulse train signals.
However, in the above-described crank angle sensor, the plurality of first and second slits are overlapped in the radial direction of the rotor plate and formed on the rotor plate. Specifically, the first slits are formed with minute lengths for the respective slits in the circumferential direction. Therefore, the manufacturing of the crank angle sensor is complex and the manufacturing operation becomes troublesome. Consequently, the cost required to manufacture such crank angle sensors becomes considerably high.
In addition, since the second slit is formed at a position of the rotor plate not related to a compression stroke top dead center position of the crankshaft, the crank angle sensor cannot discriminate one of the cylinders to be ignited during, e.g., the engine start. In this case, since the ignition is carried out on the basis of a cylinder identification signal derived from the second slit in addition to a crank angular position signal derived from the first slits, the ignition would be carried out at a time of, e.g., a suction stroke of one cylinder due to an erroneous distribution of a high surge voltage to an ignition coil.
On the other hand, a sequential injection method has been adopted in which an amount of fuel is sequentially injected at a time before the top dead center (TDC) in a compression stroke of each cylinder under a predetermined engine driving condition.
In the sequential fuel injection method, it is necessary to receive accurate information on the crank angle and cylinder identification.
Therefore, both picked-up signals of the crank angle signal and cylinder identification signal derived from the multiple number of slits installed on inner and outer peripheries of the rotor plate of the crank angle sensor are transmitted to the microcomputer. The microcomputer, then, carries out the sequential injection control during the predetermined engine driving condition on the basis of the picked-up signals and carries out, e.g., a simultaneous injection control for all cylinders during the engine start and during the engine revolution speed below a predetermined value, as exemplified by a Japanese Patent Application--Second (Examined) Publication Showa 61-60256 published on Dec. 19, 1986.
However, the crank angle sensor used in the above-described fuel injection quantity controlling system has the same drawbacks as described above.
Furthermore, a Japanese Patent Application--First Publication Showa 57-193768 published on Nov. 29, 1982 exemplifies one of the previously proposed ignition timing controlling systems.
In the previously proposed ignition timing controlling system, a correction time for the ignition timing corresponding to an angular acceleration is set to zero at a boundary of a dead zone of the acceleration/deceleration. At an outside of the dead zone, the correction time is continuously varied according to the angular acceleration with the zero being served as a base point. Therefore, a variation of an ignition timing advance angle can be suppressed which would occur in a case when the engine revolution speed becomes unstable at a time of the engine idling and the correction of the ignition timing according to the angular (crankshaft rotational) acceleration is carried out.
A controlling method in which an error of the ignition timing generated due to the angular acceleration of the crankshaft is corrected includes the steps of deriving a correction coefficient through an interpolation of a linear interpolation for each cycle and of carrying out a predetermined advance angle control on the basis of the correction coefficient.
In details, since a time it takes for the crankshaft to revolve between each reference position pulse generated from the crank angle sensor is measured and stored, a value of difference T.sub.d between the previous value T.sub.2 and present value T.sub.1 is calculated, and the correction coefficient is derived predicting the subsequent cycle only according to the difference value, a highly accurate ignition timing control is difficult to achieve over a wide range of acceleration from a low engine revolution speed to a high engine revolution speed.
In more details, FIGS. 1 through 3 show relationships between a target ignition timing during an idling with an accelerator pedal depressed and an actual ignition timing.
That is to say, in a case when an angular acceleration correction is not present, the actual ignition timing (broken line) is considerably retarded with respect to the target ignition timing (solid line) during the series of accelerations, as appreciated from FIG. 1.
On the other hand, in a case when the angular acceleration correction is carried out in the above-described method, the correction coefficient is selected so that the target ignition timing coincides with the actual ignition timing under the low engine revolution speed range. At this time, although the accuracy is improved as compared with no correction, the actual ignition timing (broken line) is retarded with respect to the target ignition timing (solid line) as the engine revolution speed is increased, as appreciated from FIG. 2.
In addition, in a case when the correction coefficient is selected so that the target ignition timing coincides with the actual ignition timing under the high engine revolution speed range, the actual ignition timing (broken line) is advanced with respect to the target ignition timing (solid line) under the low engine revolution speed, as appreciated from FIG. 3.
In this way, it is difficult to carry out the highly accurate ignition timing control at the time of acceleration in the case when the above-described correction coefficient is constant.